Driver for recessed head screws



Sept. 25, 1956 c. T. TORRESEN DRIVER FOR RECESSED HEAD SCREWS 2Sheets-Sheet 1 Filed Oct. 7; 1952 INVENTOR.

CAREL T. TORRESEN ATTORNEY Sept. 25, 1956 c. T. TORRESEN DRIVER F'ORRECESSED HEAD SCREWS 2 Sheets-Sheet 2 Filod Oct. 7. 1952 FIG.5

INVENTOR. CAREL T. TORRESEN BY. v

FIG.T

' ATTORNEY United States Patent "ice DRIVER FOR RECESSED HEAD SCREWSCarel T. Torresen, Santa Monica, Calif., assignor to North AmericanAviation, Inc.

Application October 7, 1952, Serial No. 313,488

3 Claims. (Cl. 145-50) This invention pertains to a screw and drivingtool and more particularly to an improved cross-slot screw and matingdriving tool.

A number of socket head screw arrangements have been proposed, many ofwhich have provided improved results, but none of which has completelysolved the problems involved. Ditficulties are particularly apparentwhere flathead screws are utilized which necessitate the use of arelatively shallow socket. Hexagonal type sockets are unsatisfactorybecause their depth is limited by the tapered exterior contour of aflathead screw. The driving tool will tend to round out a socket of thistype, destroying the driving faces. The usual crossslot type of screwrecess for driving operation with a complementary driving tool also hascertain unfortunate characteristics. tered is the requirement of highend pressure for keeping the screw driver in engagement with the slot.If the high pressure is not maintained the end of the driver willdisengage the slot before a driving operation is completed and the bitend of the driver may cause damage to the surface of the work. This mayeven result in a lack of ability to utilize all the fastening forceavailable from larger size screws. For example, in certain precisionwork screws should be tightened to a predetermined torque range. Forscrews of %-inch or greater diameter the end pressure required to keep atorque wrench in the driving slot will be more than it is possible forone man to exert in operating the wrench to obtain the required torque.Furthermore, the ordinary cross-slot socket head screw will raise a burralong the surface of the screw during normal driving operation and sucha burr is intolerable for many uses of the screws. These screws alsohave a large fillet at the center of the slot, with the walls of thesocket and of the screw driver arranged so that driving often takesplace at the fillet rather than along the tines of the screw driver.This results in deformation and breaking-down of the material of thescrew around the slot thus ruining the screw. 7

Therefore, it is an object of this invention to provide a screw anddriving tool requiring low end pressure during a driving operation.

Another object of this invention is to provide a screw and driving toolwhich will balance the strength of the driving tool and of the screw.

An additional object of this invention is to provide a screw and drivingtool that will operate equally well for driving the screw in eitherdirection.

Still another object of this invention is to provide a screw and drivingtool that will not form burrs in the top surface of the screw.

Yet another object of this invention is to provide a screw and drivingtool that will enable torque settings for screws of larger sizes.

A still further object of this invention is to provide a screw anddriving tool which will be usable for an indefinite number ofoperations.

The deficiency most often encoun- 2,764,197 Patented Sept. 25, 1,956

These and other objects of this invention will become apparent from thefollowing detailed description taken in connection with the accompanyingdrawings in which:

Fig. 1 is a top plan view of the cross-slot screw,

F Fig. 2 is a sectional view taken along line 2-2 of ig. 1, p

Fig. 3 is a side elevation of the driving tool,

Fig. 4 is a sectional view along line 4-4 of Fig. 3-,.

Fig. 5 is a side elevation of the screw and driver during a drivingoperation,

Fig. 6 is a sectional view taken along line 66 of Fig. 5, and

Fig. 7 is a sectional view taken along line 7-7 of Fig. 5. l

Referring to the drawings, and particularly to Figs. 1 and 2, screw 1may be of the flathead type having head portion 2 with a threaded shank3. The screw is provided with a driving socket or slot 4 in the centralportion of the head. The slot includes four driving recesses 5 whichmeet at the central i part of the screw. The recesses are equally spacedaround the top of the screw. Although illustrated'in a; generallycruciform shape wherein four driving recesses are employed, this screwcould be constructed with more or less recesses without departing fromthe scopeof the invention. Each recess 5 has two side walls 6 and 7which are parallel to the axis of the screw and extend radially outwardfrom the center of the screw. The re cesses are further defined by endwalls 8 which converge downwardly and constitute the bottom of the slot,as best shown in Fig. 2. Y

Driving tool 9 is adapted to be received within the slot of the screwfor driving the screw in. either direction. This tool may be manuallyrotatable by handle 10, or adapted for use with conventional powerdriving equipment. The driver includes a shank or bit portion 11 whichis preferably of a hardened steel material. This material shouldbe'harder than the ma.- terial of the screw head for reasons' to be mademore clear hereinafter. Bit 11 terminates in a substantially conical endor bottom portion 12. The cone may be cut off at its extremity asillustrated to provide a more or less stubby end, or it may extenddownwardly substantially to a point, as desired. The term conical asused herein is intended to include a frustum of a cone as well as aperfectly defined cone. i

The lower portion of the bit is relieved by substantially axial cutouts13 so as to form lands or tines 14 corresponding in number and spacingto recesses 5. These tines are used for driving the screw. Each tine iscomprised of two side walls 15 and 16, and an end wall 17, the latterbeing a portion of conical end 12. Edge 18 is formed where side 15 joinsend wall 17, and edge 19 where side 16 meets the end wall. It isimportant for this invention that the side walls 15 and 16 are undercut,as best seen in Fig. 3, and in the preferred embodiment they are concavein an axial direction. Nevertheless, these side walls extend radiallyoutward from the central portion of the driver, as shown in Fig. 4.

Figs. 5, 6, and 7 illustrate the driver as received within slot 4 innormal driving position with the axesof the driver and of the screw insubstantial alignment. The recesses, although substantiallycomplementary to the tines, are slightly greater in breadth so that whenthe driver is driving the screw the tines will shift to one side of theslot. This clearance permits easy engagement and disengagement of thescrew vby the driver as well as allowing angularity. Furtherprovisionfor angularity between the axes of the driver and the screw maybe made by inclining end walls 17 of the tines at a slightly greaterangle than that of end walls 8 of the recesses. By these features thedriver may be tilted relative to the screw to the position shown inphantom in Fig. 5 while still properly engaging the slot. As shown inFigs. 5, 6, and 7, the driver is in a position for rotating the screw ina clockwise direction. Edge 18 of each tine engages side wall 6 of itscorresponding recess at the extremity thereof. Engagement will obtainalong the entire length of tine because of the radial design of the tineand the recess. Because side walls and 16 of the tines are undercut, thegreatest breadth of the portion of each tine within slot 14 in everyplane parallel to the axis of the bit is along end wall 17 of the tine.When the driver is in normal driving position there will be no contactbetween the side walls of the tines and the recesses other than alongedges 18 or 19, depending on the direction of rotation, due to theundercut arrangement of the tines.

When the driver is rotated in a driving operation, as illustrated,edge-s 1 8 of the hardened bit of the driver will tend to bite into thesofter screw material along the bottom of each recess. As a result aminimum of end pressure will be required for holding the driver indr-iving engagement with the screw. This engagement of the slot by thedriver will throw up a burr along the bottom portion of each of therecesses, but this burr is desirable rather than being objectionable. Itmeans that the driver has bitten into the screw material in firmgripping engagement, and it further means that the recess has actuallybecome slightly undercut along its bottom edge, as the screw materialwas displaced. The overhanging portions of an undercut recess, when usedwith the undercut driver of this invention, will offer a resistance tothe disengagement of the driver from the screw during a drivingoperation. In fact, if manufacturing techniques permitted theireconomical fabrication, the screws for use with this invention shouldperhaps be made with undercut recesses. Recesses with axial side walls,however, are much more easily produced and provide the advantages ofundercut recesses without an attendant prohibitive cost of manufacture.The driver and screw arrangement of this invention will satisfactorilyperform a driving operation, of course, if the driver is not made of aharder material than that of the screw, but to take full advantage ofthe unique design of this invent-ion the bit should be harder than thescrew, as set forth.

Brit end 11 of the driver may be made of slightly smaller overalldiameter than the width of the slot in the screw so that the drivingends of the tines are wholly received within the slot with the top ofedges 18 and 19 disposed slightly below the top surface of the screwwhen in normal driving engagement. By this provision the burr that formswithin the driving slot of the screw will not extend beyond the uppersurface of the head of the screw.

It is obvious that the same type of driving action will take place forrotation of the screw in either direction. Thus the screw driver andscrew arrangement of this invention are equally satisfactory in bothremoving and driving a screw. In both cases the end pressure requiredwill be low. Rotation of the screw in a counter-clockwise direction willbe the same as above except that the driving force will be exerted byedges 1-9 of the tines.

It should be observed that the screw driver and screw arrangement ofthis invention provide unique opportunity for balancing the strength ofthe screw and the screw driver. The screw driver is strong because theouter portions of the tines, where the maximum driving effort isexerted, are also the thickest portions of the tines. Thus maximumstrength is at the location where it is needed most. The slot is strongbecause the recesses are relatively long and the driving force isexerted along the bottom edges of the recesses. The widths of therecesses .and of the tines may be balanced for the particular materialsused so that neither is appreciably stronger than the other.

It can thus be seen that I have provided an improved socket head screwand driving arrangement requiring low end pressure, and usable over andover again with improved rather than lessened effectiveness. Rotation ofthe screw in either direction will give the same results. Both thedriver and the screw may be designed for maximum strength and failuresof either will be minimized.

The foregoing detailed description is given by way of illustration onlyand not by way of limitation, the spirit and scope of this inventionbeing limited only by the appended claims.

'I claim:

1. A driving tool for use with a screw having a driving socket, saidsocket being defined by radially extending side walls thereby forming aplurality of recesses, said driving tool including a cylindrical bitportion terminating in a substantially conical end, said bit portionbeing provided with a plurality of substantially axially extendingrecesses therein thereby to define a plurality of tines, each tinehaving two side walls and an end wall receivable within a recess, saidside walls being concave so that within the radial limits of each ofsaid tines in all planes parallel to the axis of said bit portion thegreatest width of each of said tines is at said end wall, the edges ofsaid end wall extending radially with respect to the axis of said bit,whereby each of said tines drivingly engages said screw at the bottomportions of a recess along the edge between a side Wall and the end wallof the tine for rotation of said screw in either direction.

2. A screw driving tool comprising a shank provided with a bit ofrelatively hard material on the end thereof, said bit being providedwith symmetrically formed tines projecting from the center thereof in acruciform pattern, the end surfaces of said tines collectively defininga substantially conical shape for reception into a screw slot, the wallsof said tines at said end surfaces extending radially with respect tothe axis of said bit, the maximum width of each of said tines at saidend portion for any radial position along the tine being at said endsurface.

3. A screw driving tool comprising a cylindrical bit member of hardenedmaterial having a substantial conical end surface for reception into ascrew slot, the exterior surface of said bit being recessed axially fromsaid end surface so as to define four tines, each of said tines havingtwo edges at said end surface extending radially with respect to theaxis of said bit; the width of each tine at said end surface beinggreater than the width of any portion thereof adjacent said surface sothat each tine is given an undercut configuration adjacent each of saidedges, whereby when said end portion is received within a screw slothaving axially extending side walls said edges of said tines are adaptedto bite into said walls for rotation of said screw in either direction.

References Cited in the file of this patent UNITED STATES PATENTS685,197 Barnes Oct. 22, 1901 839,105 Butler Dec. 25, 1906 1,055,031Groos Mar. 4, 1913 1,448,392 Earnshaw Mar. 13, 1923 1,899,489 WickberghFeb. 28, 1933 2,216,381 West Oct. 1, 1940 2,285,461 Purtell June 9, 19422,369,853 Purtell Feb. 20, 1945 2,402,342 Philips June 18, 19462,445,525 Gulden July 20, 1948

